Array with light-emitting power semiconductor component and corresponding production method

ABSTRACT

A light-emitting power semiconductor device is placed on a metillic substrate structure with the formation of a good heat-transfer contact, in which a plastic protective body surrounds the power semiconductor device, leaving exposed a light exit region in the nature of a cap.

This national stage application of PCT/DE99/02750, filed Sep. 1, 1999claims priority under 35 USC 119 of the priority application, German 19841 204.5, filed Sep. 9, 1998.

BACKGROUND OF THE INVENTION

The invention concerns an arrangement comprising a light-emitting powersemiconductor device according to the preamble of claim 1 and a methodfor fabricating such an arrangement as recited in claim 17.

BRIEF SUMMARY OF THE INVENTION

It is already known to mount a light-emitting power semiconductordevice, especially a semiconductor laser, on a copper plate and tocouple the copper plate to a water cooling system for efficientdissipation of the waste heat generated in the power semiconductordevice. The connection between the copper plate and the powersemiconductor device can be made by soldering or gluing.

It is further already known to place the power semiconductor device ofsuch an arrangement in a housing to protect it against environmentalinfluences. The housing is usually formed by the copper plate itself anda metal cap seated on the copper plate and surrounding the powersemiconductor device.

The difficulties that arise in practice with this known solution chieflyrelate to the thermal and/or mechanical coupling of the powersemiconductor device to the heat sink (copper plate) and the decouplingof the useful optical output from the housing. In regard to the firstaspect, problems are created by the large difference (roughly a factorof 3) that exists between the thermal expansion coefficients of thecommonly used semiconductor materials (e.g. GaAs) and the thermalexpansion coefficient of copper. This creates the risk that theconnecting structure (solder or glue, for example) between the powersemiconductor device and the copper plate may deteriorate mechanicallyover time, causing the heat-transmission resistance to increase and, inthe extreme case, the power semiconductor device to pop off. In regardto the second aspect, in order to couple the optical laser output out ofthe housing it is necessary to have an exit window, optionally providedwith a lens, or, when an optical waveguide is being used, a waveguidefeedthrough through the metal cap. In practice, such arrangements arenot uncommonly associated with calibration problems.

Furthermore, it is disadvantageous that the aforesaid arrangement isrelatively costly to manufacture because of the metal-cap-type housingprovided with a light exit window or a waveguide feedthrough, andrequires an onerous assembly operation.

Document DE 197 06 279 A1 describes a laser device comprising a powersemiconductor device attached to a metallic base substrate. Disposed onthe metallic base substrate is a housing cover that comprises atransparent light exit region.

European patent application EP 0 869 590 A1 describes avertical-resonator laser diode placed in a housing whose floor, wallsand ceiling are made of a plastic material. An output monitoring systemis integrated into the ceiling of the housing.

Document U.S. Pat. No. 5,327,443 describes a power semiconductor lasermounted on a metallic heat sink and surrounded by a cap-like housingcover. The housing cover can be realized as a one-piece injection-moldedplastic part and comprises a transparent light exit window.

European patent application EP 0 592 746 A1 describes a laserarrangement in which a laser diode and an optical waveguide are casttogether with a casting resin. The laser diode is form-fittinglyshrouded in the cast-resin coating except on a light exit surface.

The object of the invention is to provide an arrangement that is ofsimple construction and is inexpensive to manufacture, comprising ahoused, light-emitting power semiconductor device protected againstenvironmental influences. The invention is further intended to provide amethod for fabricating such an arrangement that is simple from aproduction engineering standpoint and can be performed at low cost.

The underlying object of the invention is accomplished by means of thefeatures of claims 1 and 17.

In accordance with the invention, the power semiconductor device ishoused in a plastic protective body, the dissipation of waste heattaking place primarily via the metallic substrate structure. The plasticprotective body is made simply by injecting a hardenable plastic massonto the prefabricated substrate structure in such a way that saidstructure is coated substantially form-fittingly except on the lightexit region. The uncoated light exit region can be obtained, forexample, by means of a sacrificial part that is appropriately positionedbefore the injection step and is subsequently removed, or by means of anoptical waveguide. The metal cap used as a housing in the prior art isunnecessary. The basic advantage of the design according to theinvention is that it can be produced in a simple and inexpensive mannerand yet satisfies the practical requirements with regard to thedissipation of waste thermal power and the coupling-out of the usefuloptical output.

The plastic protective body is preferably made of a substantially opaqueplastic material. Optically transparent plastics have, for the mostpart, been found to exhibit much poorer adaptation to the thermalexpansion of the power semiconductor device during operation. Theincorporation of dispersed filler particles, especially glass particles,into the plastic protective body can favorably affect and, in somecases, further improve the thermal adaptation between the powersemiconductor device and the plastic protective body.

The plastic protective body can advantageously be made from either athermoplast or a duroplast; in practice, plastic protective bodies madefrom thermoplasts have proven to be especially suitable. However, otherplastic materials, for example casting resins or globe-top masses, havealso been used to create the plastic protective body.

The substrate structure is preferably a singulated part, particularly astamped part, fabricated of sheet metal, particularly a lead frame. Leadframes are widely used as substrates for conventional electroniccomponents and can be manufactured inexpensively in large runs withexisting production techniques. According to a preferred embodiment ofthe invention, the substrate structure is in thermal contact with acoolant, particularly water, which flows around or across at least aportion of its surface. In this way, an adequate cooling effect can beachieved even with comparatively thin-walled substrate structures. Thecoolant can also be omitted, however. In this case, heat is removed fromthe power semiconductor device via the solid heat dissipator, along orthrough the substrate structure. The substrate structure must then beheld mechanically in a suitable manner via a connection that conductsheat (away) effectively.

A variant embodiment is characterized by the fact that the substratestructure is provided with a heat-exchange body comprising microchannelsand/or microplates. Such microcoolers are known per se and aredescribed, for example, in DE 43 15 580 A1. The microchannels and/orplates can be made, for example, by laser machining, milling, punchingor electroplating, and are advantageously disposed on the underside ofthe substrate structure, in the immediate vicinity of the powersemiconductor device. Efficient thermal coupling of the powersemiconductor device to the heat-exchange body is achieved by thismeans.

According to a preferred embodiment, an optical waveguide is opticallycoupled to the light-emitting power semiconductor device and guides theemitted light out of the plastic protective body.

The optical waveguide can have light-wave guidance properties that canbe predefined to achieve certain ends, depending on the specificrequirements or application concerned. For example, the longitudinalfaces of the optical waveguide can be provided with a coating,particularly an SiO₂ coating.

In addition, suitable light-wave guidance can advantageously befurthered by internally structuring the optical waveguide to create aplurality of individual optical waveguides. Such structuring can beaccomplished in a known manner, for example by an ion-exchange method ora planar method (lateral structuring of a light-wave-guiding core layerbetween two jacket layers in the optical waveguide). In accordance withthe invention, with respect to an individual optical waveguide, thecross-sectional areas of the optical inlet and the optical exit can beselected so as to differ in size; and with respect to plural individualoptical waveguides, the geometrical arrangement of the cross-sectionalareas of the optical inlets can be configured differently from thegeometrical arrangement of the cross-sectional areas of the exits. Suchdesign measures make it possible to obtain a very specific and, ifdesired, predefinable light intensity distribution in the exit region ofthe optical waveguide.

When such an optical waveguide is provided, a process sequence that isadvantageous from a production engineering standpoint is characterizedby the fact that during the above-mentioned injection step the opticalwaveguide is completely shrouded in the plastic protective body and in asubsequent step a light exit surface of the optical waveguide is exposedin the region of the outer periphery of the marginal region, for exampleby breaking off a projecting piece of plastic material that is presenton the plastic protective body. If a spacer (a sacrificial part) is usedalternatively, instead of the optical waveguide, to create the lightexit region, in this case (i.e., where a projecting piece of plasticmaterial is present) the projecting piece of plastic material is firstbroken off and the spacer is then removed by being withdrawn.

Further preferred refinements of the invention are provided in thedependent claims.

The invention is described hereinbelow on the basis of a singleexemplary embodiment with reference to the drawing, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an arrangement according to theinvention in a side elevation;

FIG. 2 is a schematic diagram of the arrangement of FIG. 1 in plan;

FIG. 3 is a detail X of the arrangement depicted in FIG. 1;

FIG. 4 is a detail Y of the arrangement depicted in FIG. 3; and

FIG. 5 is a schematic diagram to clarify the exposure of the end face ofan optical waveguide.

DETAILED DESCRIPTION OF THE INVENTION

As depicted in FIGS. 1 and 2, an arrangement according to the inventioncomprises a substrate 1 made of copper. In the case of the substrate 1shown here, this is a TO 220 lead frame, which is used as standardpractice as a substrate for semiconductor transistors. Substrate 1 isconnected at its one end to a metal strap 2, which contacts substrate 1in the manner of an electrical lead and can further serve as amechanical retaining device for substrate 1.

Mounted on one surface of substrate 1 is a power semiconductor laser 3.Substrate 1 constitutes the first electrical terminal of powersemiconductor laser 3. Power semiconductor laser 3 is realized in theform of a laser bar that extends transversely with respect to a centrallongitudinal axis A of the arrangement, shown in FIG. 2.

On its top side, facing away from substrate 1, the bar-shaped powersemiconductor laser 3 is contacted electrically by two bonding wires 4a, 4 b. These bonding wires 4 a, 4 b constitute the second electricalterminal of power semiconductor laser 3.

Substrate 1 is equipped on its underside with an integrated microcooler(see also FIG. 3). The microcooler comprises a coolant inflow channel 5a and a coolant outflow channel 5 b, which extend in parallel and inprojection on both sides of power semiconductor laser 3. The two coolantchannels 5 a, 5 b are in fluid communication with each other via aheat-exchange body implemented as an integral, laminar structure. Inaddition to or instead of the laminar structure, other microstructures,e.g. microchannels, can be provided in the heat-exchange body. The largesurface area of the plates 6 ensures a very efficient exchange of heatbetween the plates 6 and the coolant, particularly water, flowingthrough the plates 6. As a result, the waste heat transferred from thepower semiconductor laser 3 to the substrate 1 (heat sink) can becarried off quickly and efficiently by the microcooler. The “floor”structure of substrate 1 extending between the power semiconductor laser3 and the heat-exchange body can be very thin-walled and its thicknesscan, for example, be less than 1 mm, particularly about 0.2 mm, thusproviding a short heat conduction path with little heat transmissionresistance.

Power semiconductor laser 3 is realized as an edge emitter emitting in aplane parallel to central longitudinal axis A. As described in moredetail hereinbelow with reference to FIG. 4, the emitted laser light iscoupled by means of a cylindrical lens 7 into an optical waveguide fixedon substrate 1. The optical waveguide 8 can be made of glass and, as canbe seen in FIG. 2, is implemented, for example, as an optical plate ofsquare contour, with a width in the range of 5 to 10 mm.

According to the invention, in the embodiment shown here the arrangementformed by power semiconductor laser 3, strap 2, bonding wires 4 a, 4 band optical waveguide 8 is shrouded in a plastic mass, particularly athermoplast, forming a protective housing 9. Optical waveguide 8 is runto an edge 10 of protective housing 9. It can be implemented as astructured optical waveguide in the manner described hereinabove.

In the substrate 1 shown here (i.e., a TO 220 lead frame) there is amounting opening 11, which in ordinary applications of the TO 220 leadframe is used for installing a transistor and thus is of no significancefor the present invention.

FIG. 4 is an enlargement of detail Y indicated in FIG. 3. AuSn-coated,soldered Mo sheets 12 a, 12 b are provided between power semiconductorlaser 3 and substrate 1 and between power semiconductor laser 3 andbonding wires 4 a, 4 b (not shown in FIG. 4). The AuSn solder coating isapplied to both sides of the lower Mo sheet 12 a and to at least oneside of the upper Mo sheet 12 b, i.e., the side facing in the directionof power semiconductor laser 3. The Mo sheets 12 a, 12 b serve tocompensate for mechanical stresses that arise as a result of thepreviously discussed thermal expansion mismatch between the GaAs powersemiconductor laser 3 and the Cu substrate 1 and Cu bonding wires 4 a, 4b. The described construction effects the attachment of powersemiconductor laser 3 to the substrate and the bonding wires 4 a, 4 b ina permanently mechanically and thermally stable manner. In addition, theupper Mo sheet 12 b ensures that the high operating currents that occurare distributed evenly over the surface of the power semiconductor laser3. The cylindrical lens 7 located at the emitting edge 13 of powersemiconductor laser 3, in beam path Z behind the light exit, can, forexample, be roughly 50 μm to 500 μm in diameter. It serves the purposeof concentrating or focusing the laser light exiting power semiconductorlaser 3 at edge 13 with a given ray divergence on a light inlet surface14 of optical waveguide 8, and is therefore spacedly disposed withrespect to both edge 13 and light inlet surface 14.

The position of cylindrical lens 7 can be defined by means of two stops(not shown) that are fixed on the frame and that project, with a definedspacing, from the end faces of bar-shaped power semiconductor 3 in thedirection of central longitudinal axis A past the light-emitting edge 13of power semiconductor laser 3. Said stops fixed on the frame can, forexample, be incorporated into the lower Mo sheet 12 a in a manner notshown.

To fabricate the illustrated arrangement, substrate 1 is first prepared.Said substrate 1 either can be a prefabricated, separate component (astamped part, for example), or, if lead frame technology is being used,a plurality of substrates 1 can be prepared as mounting areas in apanel-like metal sheet or a continuous metal strip (both are called leadframes). In the second case, it is advantageous that some or even all ofthe process steps in fabricating the arrangement according to theinvention can be performed in combination, i.e., jointly on the metalsheet or metal strip (lead frame).

Power semiconductor laser 3 is then attached to substrate 1 by solderingin the previously described manner and is electrically contacted bymeans of bonding wires 4 a, 4 b.

Cylindrical lens 7 is then slid so that the regions of its axial endsare against the aforesaid stops fixed on the frame, and is fastened tothe stops or to substrate 1 in this position. Thereafter—or optionallybefore the mounting of cylindrical lens 7—optical waveguide 8 isfastened to substrate 1 by gluing or the like. Finally, the clearancebetween the light inlet surface 14 of optical waveguide 8 and thecylindrical lens 7 is filled with a small drop of transparent plasticmaterial 17, for example silicone.

In the same work step, the clearance between the light-emitting edge 13of power semiconductor laser 3 and the cylindrical lens 7 can also befilled with the transparent plastic material 17. It is also possible tocover the aforesaid clearance or clearances or the entire region betweenoptical waveguide 8 and power semiconductor laser 3 appropriately insuch a way that the plastic protective housing 9 forms a cavity (i.e.,an air chamber) there. The aforesaid measures prevent plastic materialfrom the protective housing 9 from entering the beam path during theinjection step and interrupting or shadowing said path.

In an ensuing step, the protective housing 9 is put in place. Theplacement of the protective housing 9 is performed by direct injection,for example with an opaque thermoplastic material at a pressure of 80 to110 bars and a process temperature of 180° C. An anchoring recess 15 onthe substrate 1, shown in FIGS. 2 and 3, is also filled withthermoplastic material at this time. The hardening can be carried out at175° C. and takes about two hours. Other production parameters are alsopossible, depending on the plastic material used. The protective housing9 is then fixedly connected to substrate 1 via anchoring recess 15. Toform a nondetachable connection, anchoring recess 15 can be providedwith retaining teeth.

Glass particles are preferably incorporated into the liquid thermoplastbefore the injection step to favorably affect its thermomechanicalproperties.

After the injection step, a light exit surface of the optical waveguide8 is exposed at the peripheral region of protective housing 9. As shownin FIG. 5, to this end, protective housing 9 is provided with aprojecting piece 16 of plastic material that shrouds an end region ofoptical waveguide 8. The light exit surface can be produced merely bybreaking off or cutting off the projecting piece 16 of plastic material.The light exit surface can also optionally be polished subsequently toenhance its optical quality.

If the arrangement according to the invention is to be implementedwithout an optical waveguide 8, a spacer whose shape substantiallymatches that of the optical waveguide 8 is used in its place prior tothe injection step. The spacer is removed after the injection step andleaves a complementarily shaped light exit channel in the housing.

If the aforesaid process steps have been performed for pluralarrangements according to the invention in common on a lead frame, thislead frame is then (or optionally earlier, at a suitable preventiontime) separated, in a separation step, into the individual mountingareas forming substrate 1. The separation can be done, for example, bymeans of a stamping, laser-cutting or etching step.

The arrangement according to the invention can have different outputcharacteristics, as may be required. Typically, a 10 W powersemiconductor laser (useful optical output) with operating currents inthe range of 20 to 40 A is used. Up to 120 liters of water per hour canbe used to carry off the waste thermal power, which in this exampleamounts to about 20 to 40 W. High useful optical outputs of 20 W or morecan also be achieved with the arrangement according to the invention.

The arrangement according to the invention can be used in many technicalfields, it being envisaged in particular as a high-power pumped lightsource for an Nd:YAG or Yt:YAG laser.

1. An arrangement comprising a light-emitting power semiconductor device disposed on a metallic substrate structure and comprising a plastic protective body, which is formed by injection onto said substrate structure and shrouds said power semiconductor device substantially form-fittingly on the sides and top thereof, leaving a light exit region exposed, and comprising an optical waveguide that is coupled to said light-emitting power semiconductor device and that guides the emitted light out of said plastic protective body, wherein the region between said light-emitting power semiconductor device and said optical waveguide is filled, at least segmentally, with a transparent plastic material that contacts the light exit region of the power semiconductor device.
 2. The arrangement as recited in claim 1, wherein filler particles are dispersed in said plastic protective body.
 3. The arrangement as recited in claim 2, characterized in that said filler particles are present in order to adjust the thermomechanical properties of the material of said plastic protective body to the thermal expansion of said power semiconductor device.
 4. The arrangement as recited in claim 3, characterized in that the filler particles are glass particles.
 5. The arrangement as recited in claim 1, characterized in that said plastic protective body is made of a substantially opaque plastic material.
 6. The arrangement as recited in claim 1, characterized in that said plastic protective body is made of a thermoplast or a duroplast.
 7. The arrangement as recited in claim 1, characterized in that said substrate structure is a singulated part made from a panel-shaped or strip-shaped metal sheet.
 8. The arrangement as recited in claim 7, characterized in that said substrate structure is a singulated part.
 9. The arrangement as recited in claim 7, characterized in that said substrate structure is made from a lead frame.
 10. The arrangement as recited in claim 1, characterized in that said substrate structure is in thermal contact with a coolant which flows around or across at least a portion of its surface.
 11. The arrangement as recited in claim 10, characterized in that said substrate structure is provided with a heat-exchange body comprising microchannels and/or microplates.
 12. The arrangement as recited in claim 11, characterized in that said heat-exchange body is disposed in the immediate vicinity of said power semiconductor device, on the side of said substrate structure facing away from said power semiconductor device.
 13. The arrangement as recited in claim 10, characterized in that said coolant is water.
 14. The arrangement as recited in claim 1, characterized in that said optical waveguide is provided on both of its longitudinal faces with a coating for beam guidance.
 15. The arrangement as recited in claim 14, characterized in that said coating is a SiO₂ coating.
 16. The arrangement as recited in claim 1, characterized in that an optical waveguide structure creating a plurality of individual optical waveguides is formed in said waveguide.
 17. The arrangement as recited in claim 16, characterized in that with respect to an individual optical waveguide, the cross-sectional areas of the optical inlet and the optical exit differ in size, and/or, with respect to plural individual optical waveguides, the geometrical arrangement of the cross-sectional areas of the optical inlets is different from the geometrical arrangement of the cross-sectional areas of the exits.
 18. The arrangement as recited in claim 1, characterized in that to effect the optical coupling of said optical waveguide to said light-emitting power semiconductor device, a particularly reflective or diffractive lens is provided in the beam path between said power semiconductor device and said optical waveguide.
 19. The arrangement as recited in claim 18, characterized in that said lens realized as a cylindrical lens.
 20. The arrangement as recited in claim 1, characterized in that said transparent plastic material is silicone.
 21. The arrangement as recited in claim 1, characterized in that said light-emitting power semiconductor device is a semiconductor laser.
 22. The arrangement as recited in claim 21, characterized in that said light-emitting power semiconductor device is a semiconductor laser bar.
 23. A method for fabricating an arrangement comprising a light-emitting power semiconductor device, wherein the method comprises: in a first step, said light-emitting power semiconductor device is placed against and electrically contacted by a substrate structure, and in a second step that can be performed chronologically before or after the first step, an optical waveguide is affixed to said substrate structure, and in a third step, said substrate structure with said light-emitting power semiconductor device is injection-coated with a plastic mass forming a plastic protective body, wherein said optical waveguide including an exit end of the optical waveguide is completely shrouded in said plastic protective body, and in a fourth step, removing the portion of the plastic protective body that covers the exit end of the optical waveguide to expose a light exit surface of said optical waveguide at the exit end.
 24. The method as recited in claim 23, characterized in that said substrate structure is realized, at least in said first step, as a mounting area in a planar metal sheet, and the separation of the metal sheet into the individual arrangements is effected in a subsequent singulating step.
 25. The method as recited in claim 23, characterized in that as part of the fourth step, a projecting piece of plastic material integrally formed on said plastic protective body is broken off to expose said light exit surface of said optical waveguide.
 26. The method as recited in claim 23, characterized in that after said fourth step, the exposed light exit surface of said optical waveguide is polished. 